DESCRIPTION: (Adapted from applicants abstract) Workers in a variety of occupations increasingly experience fatigue as they are called upon to work extended shifts or to work shifts that bring them into conflict with the normal circadian cycles of sleep and alertness. Fatigue leads to decrements in physical and mental functioning that increase the risk of work-related musculoskeletal injury. Over the last few years, the incidence of work- related musculoskeletal injury has been increasing at the disturbing rate of 20% per year. It is the leading and most expensive occupational disorder in the country. The workers at higher risk for musculoskeletal injury are often the same workers who because of the critical nature of their jobs, when fatigued can endanger the lives of the general public they are called upon to serve. One population particularly vulnerable to these effects is firefighter/paramedics who work 24-hour shifts and whose sleep cycle is subject to unpredictable interruption by fire and medical emergencies. Once called out for an emergency, these personnel may be called upon to work under physically and mentally stressful conditions without relief for extended periods of time. Firefigher/paramedics reported that fatigue contributes to the occurrence of musculoskeletal injuries in their line of work, in which the incidence of work-related injury is 4.3 times that for private industry. It is hypothesized that physical fitness mitigates against physical and mental fatigue and that both of these variables are important precursors to musculoskeletal injury. The research investigating the linkage between fitness and fatigue is underdeveloped, with most of the work conducted in laboratory settings using artificially controlled conditions. The ultimate tests of the effect of physical fitness on work-related fatigue need to take place in naturalistic field settings where the problem actually occurs and where effective preventive strategies need to take place. The specific aims of this preliminary study are: 1) to determine the efficacy of an occupational health nursing worksite physical fitness intervention in increasing resistance to physical and mental fatigue among firefighter/paramedics by creatively extending the use of computerized measurement procedures from the laboratory to a field setting, 2) to determine individual and organizational reaction to the specific program implemented, and 3) to assess respondent burden using a repeated measures design. Using an ecologically based conceptual framework and a quasi-experimental study design, 24 non-exercising firefighter/paramedics from 4 fire departments will participate in the study: 12 firefighter/paramedics will engage in a program of aerobic condition, muscular isotonic strength training, and flexibility training for a period of 12 weeks while 12 others act as the comparison group. Physical fitness measures will include aerobic fitness and heart rate measures, muscular strength and endurance, and body composition. Fatigue measures will include measure of both physical and mental fatigue. Individual day-to-day variations in workload from participants and fire chiefs will be obtained using open-ended interviews. The information gathered in this study will provide the basis for the formulation of a larger-scale nursing intervention study that will further investigate how both fitness and fatigue affect musculoskeletal injury, the outcome of ultimate interest.